1. Field of the Invention
This invention relates to vertical oscillating spindle sanders and particularly to a tilting arbor or spindle which is vertically oscillable and driven by a variable speed hydraulic power unit.
2. Description of the Prior Art
In the past, spindle sanders using both rotary and oscillating cylindrical abrasive tools have been available. They all derive their oscillatory motion from the rotation of the spindle by means of a worm gear drive arrangement. Where a tilt of the workpiece is desired such prior art machines used a tilting table arrangement. Such machines had many drawbacks and shortcomings. Generally prior art machines had a single speed electric motor drive although a few had two speed electric motor drives. With a single speed certain operations are very slow, e.g. when working with a small diameter sanding sleeve, the surface speed per minute is very low. Conversely when slow material removal is an advantage, as where accuracy and control are important, this single speed can be a decided disadvantage, especially where it is desired to use a large diameter sleeve for a particular part contour. A two speed machine can be of some advantage here but only in a limited fashion. A single oscillating speed must also be accepted in a single speed machine or two with a two speed machine. This severely limits the yield and productivity of the machine. A tilting table puts an undue load on the operator who is trying to hold the work on the table while sanding. All of these disadvantages or shortcomings compromise the safety of the operator, the yield and productivity of the process and are less than desirable.
Typical of the prior art machines are U.S. Patents to Downer U.S. Pat. No. 1,259,494, Bjorklund U.S. Pat. No. 1,762,606, Monson U.S. Pat. No. 1,881,839 and McEwan U.S. Pat. No. 3,418,758. All of these machines suffer from the drawbacks discussed above. Most particularly they cannot match the speed with the work and are disadvantageous on that account above. None of the prior art has an adjustable spindle and none of the prior art shows a spindle of infinite variation from near zero to the limit desired by the operator.